As Happyfish has mentioned, the printer should include the 2-inch roll holder.
If you're not in the mood to drop another several hundred bucks right away for the 3-inch holder (Why, Canon, why?!), you can use the 2 inch holder for 3-inch core papers. Just mount the paper as usual and load it up. It will unravel a marginal amount, and it'll be more of a pain to remove the paper when you're done, but it works.